Modeling rhizosphere carbon and nitrogen cycling in <i>Eucalyptus</i> plantation soil

Vigorous Eucalyptus plantations produce 105 to 106&thinsp;km&thinsp;ha−1 of fine roots that probably increase carbon (C) and nitrogen (N) cycling in rhizosphere soil. However, the quantitative importance of rhizosphere priming is still unknown for most ecosystems, including these plantations. Therefore, the objective of this work was to propose and evaluate a mechanistic model for the prediction of rhizosphere C and N cycling in Eucalyptus plantations. The potential importance of the priming effect was estimated for a typical Eucalyptus plantation in Brazil. The process-based model (ForPRAN – Forest Plantation Rhizosphere Available Nitrogen) predicts the change in rhizosphere C and N cycling resulting from root growth and consists of two modules: (1) fine-root growth and (2) C and N rhizosphere cycling. The model describes a series of soil biological processes: root growth, rhizodeposition, microbial uptake, enzymatic synthesis, depolymerization of soil organic matter, microbial respiration, N mineralization, N immobilization, microbial death, microbial emigration and immigration, and soil organic matter (SOM) formation. Model performance was quantitatively and qualitatively satisfactory when compared to observed data in the literature. Input variables with the most influence on rhizosphere N mineralization were (in order of decreasing importance) root diameter&thinsp; &gt; &thinsp;rhizosphere thickness&thinsp; &gt; &thinsp;soil temperature&thinsp; &gt; &thinsp;clay concentration. The priming effect in a typical Eucalyptus plantation producing 42&thinsp;m3&thinsp;ha−1&thinsp;yr−1 of shoot biomass, with assumed losses of 40&thinsp;% of total N mineralized, was estimated to be 24.6&thinsp;% of plantation N demand (shoot&thinsp;+&thinsp;roots&thinsp;+&thinsp;litter). The rhizosphere cycling model should be considered for adaptation to other forestry and agricultural production models where the inclusion of such processes offers the potential for improved model performance.</p

Increase in cation exchange capacity by the action of maize rhizosphere on Mg or Fe biotite-rich rocks.

O intemperismo de alguns minerais silicáticos em rochas moídas pode ocorrer em alguns dias de cultivo e gerar diferentes propriedades físico-químicas, com benefícios potenciais a solos tropicais. Objetivou-se investigar a influência da rizosfera do milho (Zea mays L.) nos produtos do intemperismo e na capacidade de troca de cátions da biotita-Mg da biotita xisto e biotita-Fe da biotita sienito. Um experimento em vasos foi conduzido de forma que plantas e rochas moídas foram avaliadas por sete ciclos de cultivo sucessivos. Os nutrientes ferro e potássio foram adquiridos da biotita xisto e da biotita sienito durante o cultivo. O intemperismo das biotitas promovido pela rizosfera causou mudanças mineralógicas. A mudança mais expressiva nos padrões da difração de raios-X ocorreu na fração com partículas < 53 &#956;m, mas as frações 53-300 &#956;m também mudaram. A alteração na biotita-Mg, que possui menor relação Fe/Mg nos sítios octaedrais que a biotita-Fe, foi responsável pelo maior aumento na capacidade de troca de cátions nas frações < 300 &#956;m. Entretanto, o processo de intemperismo da biotita-Fe, a qual apresenta alta relação Fe/Mg nos sítios octaedrais, não aumentou a capacidade de troca de cátion

Successive off take of elements by maize grown in pure basalt powder.

Abstract: Basalt powder wastes from mining activities have potential to be used as a natural fertilizer. Basalt minerals in agricultural soils may release plant nutrients and increase soil negative charge. In this work, the weathering of basalt promoted by maize rhizosphere was investigated. We studied the chemical and mineralogical composition of basalt, including cation exchange capacity, as well as the rate of elements offtake by maize grown in a pure basalt powder during seven successive growth cycles. A pot experiment was carried out under controlled environmental conditions; plant and rock materials were evaluated at the end of successive growth cycles. X-ray powder diffraction analysis showed diopside and andesine as main minerals of basalt, and smectite. Scanning electron microscopy images evidenced new amorphous components resulting from rhizosphere-induced weathering. The elements K, Ca, Mg, Al, B, Cu, Fe, Mn and Zn were measured in plant tissue, and related to the weathering of basalt minerals. The studied basalt, therefore, provides nutrients to plants and exhibits physicochemical properties, such as cation exchange capacity, especially important for highly weathered soils presenting low cation exchange capacity, such as Oxisols.Article Number - 9A4418A6291

Strike-slip faults mediate the rise of crustal-derived fluids and mud volcanism in the deep sea

We report on newly discovered mud volcanoes located at ∼4500 m water depth ∼90 km west of the deformation front of the accretionary wedge of the Gulf of Cadiz, and thus outside of their typical geotectonic environment. Seismic data suggest that fluid flow is mediated by a >400-km-long strike-slip fault marking the transcurrent plate boundary between Africa and Eurasia. Geochemical data (Cl, B, Sr, 87Sr/86Sr, δ18O, δD) reveal that fluids originate in oceanic crust older than 140 Ma. On their rise to the surface, these fluids receive strong geochemical signals from recrystallization of Upper Jurassic carbonates and clay-mineral dehydration in younger terrigeneous units. At present, reports of mud volcanoes in similar deep-sea settings are rare, but given that the large area of transform-type plate boundaries has been barely investigated, such pathways of fluid discharge may provide an important, yet unappreciated link between the deeply buried oceanic crust and the deep ocean